The present invention is directed to a light engine package in which light is generated from a light emitting diode (LED), and more particularly to a light engine package that produces light of a particular color using a phosphor and LED in combination.
An LED package that produces white light typically includes a blue-emitting LED embedded in a transparent polymer, such as silicone, where the polymer is either coated or impregnated with a yellow-emitting phosphor. A typical blue-emitting LED is GaN-based with an InGaN active layer that emits blue light with a wavelength of 450 to 470 nm. The yellow-emitting phosphor may include cerium-doped yttrium aluminum garnet. Part of the blue light from the LED is converted by the yellow-emitting phosphor to a spectrum of light centered at about 580 nm (yellow). This yellow light and the remaining blue light together give the appearance of white light.
Alternatively, the LED package may include LEDs and phosphors of other colors (e.g., red and green LEDs and/or red-emitting and green-emitting phosphors) to produce LED packages with particular colors other than white.
In any event, the polymer is formed on (typically molded onto) the LED so that the package includes an integral arrangement of the polymer and LED (see, for example, U.S. Pat. No. 6,577,073 in which a blue-emitting LED is molded in a material impregnated with a yellow-emitting phosphor and U.S. Pat. No. 7,213,940 in which a blue-emitting LED is encapsulated in a polymer.) This integral arrangement causes problems because the phosphor proximity to the LED leads to heat-induced lumen degradation. Thus, applications including LED packages with a phosphor require a thoughtful thermal design. Further, the formation of the polymer on the LED reduces the flexibility of application of LED packages.
It would be beneficial to develop an LED package that avoids the heat problems of the prior art and that affords more flexibility for lighting designers.